Filter trimming

Abstract

The invention relates to trimming of analogue filters ( ) in integrated circuits by means of an automatic adjusting circuit. A local oscillator ( ) in the automatic adjusting circuit provides a periodic reference signal (R) to an adjustable phase shifter ( ), which on basis thereof, produces a periodic phase shifted signal (R*). A phase detector ( ) receives both the periodic reference signal (R) and the phase shifted period signal (R*) and produces a test signal (T) in response to a phase difference between the periodic reference signal (R) and the periodic phase shifted signal (R ). A lowpass filter ( ) receives the test signal (T) and generates a level signal (T ) relative a reference level, e.g. representing a zero voltage. A digital signal processor ( ) produces a primary control signal (C ), having a serial format, on basis of the observation signal (M). A serial-to-parallel converter ( ) converts the primary control signal (C ) into a control signal (C ) having a parallel signal format. The control signal (C ) influences a magnitude of at least one component value in the adjustable phase shift between the periodic reference signal (R) and the periodic phase shifted signal (R*) attains a calibrated value being as close as possible to a desired value. A latch ( ) forwards at least one signal element of the control signal (C ) for setting of at least one component value in the analogue filter ( ) in accordance with a setting of at least one component value in the adjustable phase shifter ( ) which produces the calibrated value.